ANIMAL KINGDOM. 297 



to be consulted rather for the observed facts they may 

 contain, than for the inferences that may be drawn from 

 those facts respecting arrangement. 



In comparing animals of the same natural group we al- 

 ways find the terrestrial to be more perfectly organized than 

 the aquatic. Thus in the animal kingdom we have found 

 Insects and Mammalia to be removed the furthest from the 

 vegetable kingdom ; and again, in observing the vertebrated 

 animals, we have found fishes to be the most imperfect of 

 the group. It may therefore, perhaps, be concluded that 

 though the Crustacea have a distinct system of circulation, 

 yet, when considered with reference to the externally ar- 

 ticulated animals in general, they are not so perfectly con- 

 structed as those insects which are terrestrial. Indeed the 

 system of circulation in the Crustacea, being so different 

 from what is observed in Insects, shows that the former 

 have quitted the type of their peculiar group in order to 

 acquire an imperfect sketch of the circulation of the Ver- 

 tebrata ; and as to the method of respiration, there is every 

 reason to believe that this depends on the medium in which 

 the animal lives, and that water is the medium which 

 requires the greatest similarity in the structure of the re- 

 spiratory organs. This hypothesis is supported by the 

 well known fact, that those larvae of insects which live in 

 water are furnished with branchiae exactly of the same 

 structure with those of some aquatic Annelides, while the 

 remainder of their respective structures are almost at total 

 variance. At all events, though deprived of a distinct sy- 

 stem of circulation, insects are the most lively of the An- 

 nulosa, and the most perfectly endowed with all the five 

 senses. 



I would also remark, that all Annulose animals have 



